In Vitro and in Vivo Estrogenicity and Toxicity Ofo‐,m‐, Andp‐dichlorobenzene

The estrogenicity of o‐, m‐, and p‐dichlorobenzene (DCB) was evaluated with a yeast estrogen screen (YES) and zebrafish (Danio rerio) vitellogenin (VTG) assays. With the YES, p‐DCB and m‐DCB were found to be estrogenic in a concentration‐responsive manner. The relative potency measured with the YES (relative to 17β‐estradiol) was 2.2 × 10−7 for p‐DCB and 1.04 × 10−8 for m‐DCB. Following acute toxicity tests with the zebrafish, plasma VTG production was measured to examine the in vivo estrogenic activity of the three compounds after a 14‐d exposure. Adult zebrafish were exposed to different concentrations of o‐, m‐ and p‐DCB, ranging from 0.1 to 32 mg/L; ethynylestradiol ([EE2]; 5 ng/L, 10 ng/L, 50 ng/L, and 100 ng/L) was used as a positive control. After exposure, blood samples were taken and protein electrophoresis was performed to determine the relative VTG content. Gonadosomatic indices (GSI) and condition factors (CF) were also calculated. Elevated VTG levels and decreased female GSIs were found in fish exposed to ≥5 ng EE2/L and in fish exposed to ≥10 mg p‐DCB/L. Low GSIs coincided with high levels of VTG in the blood of female zebrafish. This relation was not only found in fish exposed to EE2 but also in controls and fish exposed to DCB. Therefore, a direct or indirect effect of VTG on the GSI is suggested rather than a direct toxic effect of the tested compounds on the gonads.